Meeting Abstract
We surveyed 22 populations of Mojave desert tortoises (Gopherus agassizii) across their range in the spring seasons of 2010-2012. In addition to testing for visible severity of respiratory disease, prevalence of the pathogen Mycoplasma agassizii, and infection intensity, we quantified bacteria-killing ability (BKA) of blood plasma and differential white blood cell numbers in the peripheral blood. Principal component analyses of these immunological measures indicated the variation was mostly explained by two PCs, PC1 representing inflammatory processes and PC2 representing specific responses not immediately associated with inflammation (largely driven by lymphocyte numbers). Climatic variables were calculated from NOAA weather stations and PRISM data. Model selection and Akaike criteria indices were used to evaluate which climatic and/or immunological variables may be important in affecting prevalence of M. agassizii, mean infection-intensity of M. agassizii, and visible disease among populations. Lymphocytes were strongly associated with decreased loads of M. agassizii and cooler thermal regimes. While clinical signs of disease were not associated with lymphocytes, they were associated with PC1, representing inflammatory processes. This study suggests that tortoises may use multiple immune functions to control M. agassizii, and that lymphocyte function may reduce pathogens without initiating the inflammatory processes that leads to observable disease. Because lymphocytes are known to have a phagocytic function in reptiles, the temperature-dependence of both antibody production and phagocytosis by these cells should be addressed in future experiments.
